The project seeks an understanding at the molecular level of cystine storage disease or cystinosis, an inherited disease of children which invariably results in uremic death early in life. Since skin fibroblasts from cystinotic patients have 100 times the normal cystine content, these cultured cells serve as an excellent model for biochemical investigation of this fatal disease. The influx and efflux of S35 L-cystine and the intracellular metabolic conversions have been determined and the data show the rapid accumulation of labeled cystine in cystinotic cells. The transport of S35 labeled cysteine and methionine as well as their intracellular metabolism are to be studied in a search for differences in the handling of sulfur amino acids by normal and cystinotic cells. The kinetic properties of the enzyme involved in reduction of cystine, GSH-cystine transhydrogenase, has been delineated, and further studies will encompass the isolation of the intermediate products of the reaction. An investigation of the activity of other enzymes involved in sulfur amino acid metabolism will be undertaken. Electron microscopic analysis to delineate intracellular localization of stored cystine in cultured cells originating from organs from a cystinotic aborted fetus suggest the inclusion of cystine crystals within mitochondria. Determination of activities of lysosomal acid hydrolases have shown the effects of intracellular cystine on the several enzymes investigated leading to the application of the antigen-antibody precipitation technique for isolation and structural analysis and quantitation of specific lysosomal enzymes in normal and cystinotic cells. BIBLIOGRAPHIC REFERENCES: Cystinosis in the Fetus and Placenta: The Anatomic Distribution of Cystine In Utero by Billy E. Buck, Beatrice States, Klaus Hummeler, and Stanton Segal. J. Pediatrics, Accepted, November, 1975.